Irregular & delayedperiod

Asked for Female, 20 Years

My periods just not came since 2.5 months.
But I had a urine test (pregnancy) at a test lab and it showed a negative result.
So I want to know what is the way or remedy to have periods fast and is this test which i had gives full 100% assurance that it is correct?
What should I do so i don't face this problem again?